nande
Nande (なんで) is a Japanese interrogative adverb meaning "why" or "how come." It is the casual equivalent of more formal words such as doushite (どうして) or nazé (なぜ). Used to ask for the reason behind an action, event, or situation, it is common in spoken Japanese and informal writing.
Etymology and form: なんで is written as 何で in kanji, and is read as nan de in some contexts
Usage: Nande is typically placed at the beginning of a question or inside it. Examples include "なんで学校を休んだの?"
Register and nuance: Nande is informal and best suited to conversations with friends, family, or peers. In